The long-term goal of this project is to identify novel monoclonal antibodies (mAbs) that broadly recognize the HIV-1 envelope glycoprotein (Env) and block infection in vitro to guide vaccine development. This goal will be pursued in a cohort of HIV-1 infected individuals who control their infections in the absence of anti-retroviral therapy (Natural Virus Suppressors/NVS) and who have circulating broadly neutralizing antibodies (broad nAbs). A key element of our approach is the development of a new assay to census Env-specific memory B cell clones (BMem) that allows the rapid and direct cloning of full-length monoclonal antibodies (mAbs). These mAbs will be characterized for epitope specificity and neutralization breadth to create clonal profiles of the BMem that are generated during the control of HIV-1 infection. This information will be used to test the hypothesis that neutralization breadth is determined by a polyclonal response comprised of a mosaic of neutralizing specificities as opposed to a pauciclonal response comprised of one or a very few neutralizing specificities. Testing this hypothesis is key to our long-term goal of identifying novel mAbs that broadly recognize Env and block infection in vitro to guide vaccine development against HIV-1. There are two specific aims. Aim 1- To develop clonal specificity profiles of Env-specific BMem from NVS who have ongoing broadly neutralizing antibody responses- Clonal specificity profiles of anti-Env responses will be determined by limiting dilution analysis, mAb isolation, and epitope mapping to determine the relative dominance of BMem clones specific for different Env-epitopes. Aim-2- To compare neutralization breadth between plasma antibodies and mAbs representing a full clonal profile of BMem to determine the number of mAbs that must be pooled to reconstruct the neutralization breadth of the circulating antibody pool. This data will be used to determine the clonality of an ongoing broad nAb response. This aim will complete testing the hypothesis that neutralization breadth is determined by a polyclonal response comprised of a mosaic of neutralizing specificities as opposed to a pauciclonal response comprised of one or a very few neutralizing specificities. Currently there is no vaccine against AIDS. The work proposed in this application will investigate how some people control HIV-1 infection for many years without anti- retroviral drug therapy. This information should be useful in making a vaccine against AIDS.